Interface - The Journal of Wheel/Rail Interaction

PERFORMANCE-BASED ASSESSMENT

Using Performance-Based Assessment of Reserve Gauge Strength to Enhance Tie-Replacement Planning
By Robert Madderom • April 2009

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Technology has changed the ways in which railroads plan most of their maintenance programs over the past 30 years. But one aspect of maintenance planning has remained static. Railways still select ties for replacement and plan a significant portion of their maintenance budgets based on visual inspections by walking tie inspectors.

Modern technology is used to monitor track and component conditions in order to effectively plan and budget for maintenance requirements. Laser and optical systems are used to measure wheel and rail wear. Ultrasonic technologies can detect rail flaws before they mature. But in 150 years of railroading, little has changed in terms of crosstie renewal.

Crosstie replacement and spot maintenance programs are based on visual inspections, field experience, and (on some railroads) tagging and classification via various software tools. But the overall assessment is still based on visual inspection. Because of this, inspections are more subjective than they should be, and judgment by inspectors can vary by as much as 20%. These shortcomings can have a major impact on the goal of any crosstie evaluation program, which is to meet the track class requirements and to do so by maximizing the economic value of every tie in the budget.

Figure 2 illustrates the concept of the Optimal Economic Track Condition. Clearly, railroads cannot effectively operate with all of their track at minimum safety standards, represented here by the pink line. The figure also indicates that Optimal Track Condition is significantly higher at higher track classes, tonnage and speed, and with a higher factor of safety. The yellow line represents theoretical ineffective tie replacements. If too many ties are replaced in this Class 2 track, budget dollars are wasted. If too few ties are replaced, the track will under-perform, requiring additional monies to achieve the desired condition — again, a poor use of budget.

Simply put, removing a tie too early results in lost value; leaving behind too many weak ties requires additional spending. For heavy-tonnage, high-speed tracks, the “get ‘em all” approach makes sense, because of the need to ensure that the track condition can safely support the traffic and tonnage. On lower track classes, the process of deciding how many and which ties should be replaced is more challenging.

Since most railways devote 25% - 30% of their maintenance budgets to tie activities, the value of optimizing a tie renewal program can be significant. Part of the problem that railways face, however, is that they have no way to measure the lost value of a tie that is replaced too early. Even a 5% misallocation of the tie budget can represent a significant loss of long-term value. Every tie that is inserted is an investment that needs to be utilized correctly in order to obtain the optimal economic benefit from limited budgets.

Technology Can Help
Over the past 20 years, Gage Restraint Measurement Systems (GRMS) have been used to quantify the reserve track gauge strength — a key parameter in the selection of crossties for replacement or maintenance. GRMS was originally developed as an alternative standard for minimum safety. The Track Safety Standards Part 213.110 outlines the use of this standard as an alternative to the requirements of “tie and fastener counting” sections (213.109 and 213.127).

As a minimum safety standard, GRMS has generally been thought of as something to use in lower track classes where the railroad is trying to limit tie expenditures. The performance-based GRMS method of assessment can do that quite effectively. But more can be done.

Almost 100,000 miles of track are tested for gauge strength annually in North America, today. But only about 2% of the GRMS testing is used to support the alternative Part 213.110 standards. The remaining 98% is primarily used for short-term track maintenance. GRMS is not utilized to its full potential in terms of crosstie renewal programs.

Reserve gauge strength data has the potential to provide additional information to support and develop effective tie-replacement programs. The key measurement for such programs is “Gage Widening Projection” (GWP). GWP is a replacement for the “Gage Widening Ratio” (GWR) in the Part 213 track minimum safety standards, and is currently the best objective, performance-based measurement of the ability of ties and fasteners to hold gauge.

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